1. Field of the Invention
The present invention relates to a balance shaft housing, and more particularly to a housing for accommodating balance shafts provided with counterweights for canceling out a vibromotive force caused by pistons.
2. Description of the Related Art
For example, JP-B-5-39233U discloses a balancing device in which balance shafts provided with counterweights for canceling out a secondary vibromotive force generated by pistons of an engine are disposed below a crankshaft within an oil pan and in which the rotation of the crankshaft is transmitted to the balance shafts via a chain/sprocket mechanism or a gear mechanism.
Since the balance shafts of the balancing device are provided below the surface of lubricating oil in the oil pan, in order to prevent the occurrence of inconveniences caused by lubricating oil stirred by the balance shafts, the balance shafts are fully covered by the housing. In addition, when a great amount of lubricating oil stay within the housing, since it constitutes resistance to the rotation of the balance shafts, the lubricating oil within the housing must be discharged without any delay, and the aforesaid patent publication discloses the balance shaft housing constructed such that the lubricating oil within the housing is discharged by the rotating balance shafts.
According to the construction disclosed in the above patent publication, however, the discharge ports for lubricating oil are made open upwardly, and therefore, this construction facilitates the entering into the housing of lubricating oil dropping from the cylinder block. Thus, the efficiency at which lubricating oil is discharged from the interior of the housing cannot be improved. Additionally, in the event that there are provided openings, additional means is needed for securing the rigidity of the housing, and this tends to complicate the configuration of the housing itself.
The invention was contrived with a view to solving the drawbacks inherent in the related art, and a primary object thereof is to provide a balance shaft housing which is constructed so as to prevent the intrusion into the housing of lubricating oil dropping from the cylinder block side while maintaining the rigidity as high as possible.
With a view to attaining the object, according to a first aspect of the invention, there is provided a balance shaft housing (an upper housing 14U, a lower housing 14L) disposed in an oil pan (7) For accommodating balance shafts (13L, 13R) provided with counterweights (19) for canceling out a vibromotive force caused by pistons, characterized in that the housing comprises housings which are divided along a plane which is parallel with the balance shafts, and gaps (37) are formed between edge surfaces of respective side walls of the divided housings which are brought into contact with the plane for discharging lubricating oil from the housing, and that eaves-like projecting portions (38) are integrally formed on the upper housing (14U) of the divided housings for covering the surfaces confronting the gaps. According to this construction, the eaves-like projecting portions help not only prevent lubricating oil from flowing into the housing but also enhance the rigidity of the housing without involving an increase in number of components.
In addition, according to a second aspect of the invention, the eaves-like projecting portions are connected to bearing portions (a second bearing wall 26, a bearing hole 40) provided on the upper housing for supporting the balance shafts, whereby the rigidity of the bearing portions can be enhanced. According to a third aspect of the invention, the eaves-like projecting portions are connected to an axial position regulating portion (a thrust bearing wall 16) for the balance shafts which is provided on the upper housing, whereby the rigidity of the axial position regulating portion can be enhanced. According to a fourth aspect of the invention, the eaves-like projecting portions are connected to fastening portions (boss portions 39) which are provided on the upper housing for fastening the lower housing, whereby the rigidity of the fastening portion can be enhanced.
On top of the above constructions, according to a fifth aspect of the invention, the edge surfaces of the respective side walls of the divided housings which are brought into contact with the dividing plane are offset from each other to thereby form the gaps, whereby the reduction in strength of the side walls otherwise resulting from the provision of lubricating oil discharge ports is substantially eliminated, thus the rigidity of the housing being able to be enhanced as a whole.